Recently, due to increased interest in environment-friendly materials, proposals have been made to use natural materials in various kinds of industrial products. For example, a housing for lap-top computers, made of a bioplastic material, has been proposed. From the point of view of being decorative in addition to being environment-friendly, natural wood is used in various kinds of industrial products. For example, natural wood is used for finishing or armored surfaces of bags and the like and for housings of electronic equipments such as calculators. There is active study to utilize the natural materials for the housings of electronic equipments, and in particular, natural wood that has decorative grains.
Conventionally, in the wood products or partially wood products, the wood is impregnated with a specific resin in order to improve the applicability. In addition, techniques, such as pressing, have been developed in order to process the wood into a desired shape.
When using the wood material for the finishing or armored surface of the housing used for PDAs (Personal Digital Assistants), PCs (Personal Computers) and the like, the decorative feature of the wood grain may be an important basic feature. Typically, the wood material used for the finishing or armored surface should not include exposed surface defects, such as worm-eaten parts, rotted parts, split parts, and scratches. For this reason, most thinnings are excluded from use for the finishing or armored surface. In addition, defects such as splits and cracks should be avoided when forming the housing or after forming the housing. If the defect is generated when the housing is formed or after the housing is formed, the wood material may no longer be suitable for the housing as a product having commercial value, even though the wood material was originally suited for the housing.
Further, a heat generating element, such as a semiconductor device, may be provided in the housing of the electronic equipment. For this reason, the housing is required to satisfy a fire-resistant standard. Thus, when using the wood material for the housing having such a requirement, the heat generating element is covered by an enclosure made of a fire-resistant material, such as a metal plate. Alternatively, the wood material is coated or impregnated with a fire-resistant agent in order to make the wood housing itself fire-resistant.
Next, a description will be given of a method of forming processed wood having a curved part, by referring to FIGS. 1A through 1F. FIGS. 1A through 1F are cross sectional views for explaining an example of the method of forming the processed wood having the curved part.
First, as illustrated in FIG. 1A, a plurality of wood plates (or plywood) 11 are stacked via an adhesive agent 12, and the wood plates 11 are bonded together to form a provisionally stacked plywood 13. The provisionally stacked plywood 13 is softened in a water vapor environment 14. From the point of view of efficient utilization of resources and/or minimizing costs, thinnings may be used for the wood plates 12, even though the thinnings often include parts with different densities such as gnarls and/or parts with different brittleness. In addition, the thinnings may be used only for the wood plates 12 between the two outermost wood plates 12 forming the finishing or armored surfaces,
As illustrated in FIG. 1B, the provisionally stacked plywood 13 that is softened is inserted between a female die 15-1 and a male die 15-2 of an exclusive metal form die 15, and is formed into a workpiece 16 having curved parts, as illustrated in FIG. 10.
The dies 15-1 and 15-2 are separated in order to obtain the workpiece 16 made of the plywood, as illustrated in FIG. 1D. The workpiece 16 is chamfered in order to obtain a chamfered member 18 illustrated in FIG. 1E. Thereafter, the chamfered member 18 is impregnated with a flame retardant (or a fire-resistant agent), in order to obtain a wood workpiece 19 having the curved parts, as illustrated in FIG. 1F.
However, when using the metal form die 15 illustrated in FIG. 10, stress is concentrated at the curved parts of the provisionally stacked plywood 13 and thus at the curved parts of the workpiece 16. Consequently, a split or crack 17 may be generated at the curved part of a workpiece 16′, as illustrated in FIG. 2. FIG. 2 is a cross sectional view for explaining a split or crack generated at the curved part of the workpiece. In addition, a crack and/or warp may be generated at parts with different densities such as gnarls and/or parts with different brittleness, which may exist locally in the case of natural wood. Moreover, when the chamfered member 18 is impregnated with the flame retardant in FIG. 1F, a warp or strain may be generated in the wood workpiece 19 due to moisture absorption. Particularly when a gnarl exists inside the wood workpiece 19, the impregnation state may become different between the gnarl and parts surrounding the gnarl, to thereby increase the warp or strain. These problems may depend on the kind of wood and/or the quality of wood used, and it may be difficult to suppress inconsistencies in the wood workpiece 19 that is fabricated.
Therefore, according to the technique that stacks a plurality of wood plates and forms the curved parts by pressing, the crack and/or warp may be generated at the curved part and/or the uneven quality part of the wood when the curved part is formed by pressing, to thereby deteriorate the yield. In addition, when the wood material is impregnated with the flame retardant, the warp and/or strain may be generated due to the quality of wood or the unevenness of the wood quality, to thereby also deteriorate the yield. Such deterioration in the yield increases the fabrication cost of the wood housing, and may prevent the use of natural wood for the housing of the industrial products such as electronic equipments. Moreover, when a fire-resistant enclosure is provided within the housing instead of impregnating the wood material of the housing with the flame retardant, the housing structure may become bulky or thick. Further, the number of parts increases due to the provision of the fire-resistant enclosure, to thereby increase the fabrication cost of the wood housing.